Evolution: Diversification of Angiosperm Rooting Systems in the Early Cretaceous

First author: Alexander J. Hetherington; Affiliations: University of Oxford (牛津大学): Oxford, UK

Corresponding author: Alexander J. Hetherington

Summary    A monocot from the Early Cretaceous developed a cluster of anatomically similar roots from the base of a stocky stem. This discovery indicates that angiosperm rooting systems were more diverse than previously thought at this time. 

Most fossils of angiosperm roots from the Early Cretaceous that have been described to date are described as adventitious and developed from horizontal shoot axes called rhizomes (Figure 1). Rhizomes of many extant herbaceous plants grow horizontally through the surface of soil and develop roots that supply water and nutrients as well as tethering the axis to its growth substrate. Leaves, vertically growing (orthotropic) shoots and often roots develop along rhizomes forming ramifying branched systems. The prevalence of this bauplan — root-bearing rhizomes — in the Early Cretaceous fossil record supports the hypthosis that early angiosperms developed a rhizotamous habit. The recent paper by Coiffard et al. describes a new Early Cretaceous monocot species, Cratolirion bognerianum, revealing that there was at least another type of rooting system present in the Early Cretaceous. The description of the fossil C. bognerianum demonstrates that rooting systems were more diverse than previously thought in the late Aptian to early Albian just over 100 million years ago.

一个白垩纪早期的单子叶植物从一个茎干的基部发育出了一簇在解剖学上类似于根的组织。 这一发现表明，被子植物生根系统比以前认为的要更加多样化。迄今为止，大多数已发现的白垩纪早期被子植物根的化石都属于不定根，并从根茎的水平茎轴发育而来（图1）。许多现存的草本植物的根茎在土壤的表面水平生长，并发育出根组织，以供应植株水分和养分以及将整个植株固定在生长基质上。垂直生长的叶片以及通常沿着根茎发育的根组织一起形成了分枝系统。白垩纪早期的化石记录表明了这种能够形成根的根茎组织的普遍性，支持早期被子植物发育出根茎特征的假说。 Coiffard等人的最新论文描述了一种新的白垩纪早期单子叶植物物种Cratolirion bognerianum的化石，揭示了白垩纪早期至少存在另一种生根系统。Cratolirion bognerianum的化石描述表明，大约在一亿年前的早阿普第期到晚阿普第期早期被子植物的生根系统要比之前所认为的更加多样化。

通讯：Alexander J. Hetherington  (https://www.kribb.re.kr/eng/sub02/sub02_03_01.jsp)

个人简介：布里斯托大学，硕士；牛津圣凯瑟琳学院，博士。

研究方向：植物根系的起源与演化。

doi: https://doi.org/10.1016/j.cub.2019.08.030

Journal: Current Biology

Published date: October 21, 2019